This invention relates generally to a device which separates what is usually called the heavier and lighter fractions of a liquid sample. More particularly, this invention relates to devices or assemblies utilizing an evacuated tube placed under centrifugation wherein a liquid sample is placed in the tube, and subsequently the tube is subjected to centrifugal force in order to cause the heavier fraction (or the fraction having the higher specific gravity) to the closed end of the tube while the lighter fraction (or that fraction having a lower specific gravity) moves toward the open end of the tube.
Such arrangements utilize some sort of barrier for moving into the area adjacent the two phases of the sample being separated in order to maintain the components separated for subsequent examination of the individual components. The thrust of all of the devices developed for use in the environment discussed above is to provide a barrier which divides cleanly the heavier and lighter fractions of the sample being separated.
When taking blood samples for test purposes, for example, whole blood generally is drawn into an evacuated collection tube, and the tube is centrifuged to separate the blood into the relatively lighter phase or component, as discussed above which is serum or plasma, and a heavier cellular phase. A variety of mechanical devices have been utilized in the past including piston-type arrangements for moving freely in the liquid sample in the evacuated tube so that the piston arrangements subsequently come to rest in the divided area between the heavier and lighter phases. While these mechanical arrangements have proved useful in a limited sense, they have not been entirely successful because they do not provide the clean separation discussed above.
The material utilized generally at this time for providing the barrier or separation between the heavier and lighter phases or the components having the lower and higher specific gravities include various thixotropic gel materials or sealants such as those described in U.S. Pat. No. 3,852,194, which is a mixture of silicone and hydrophobic silicon dioxide powders. Another form of thixotropic gel is a polyester gel which is presently utilized for a great many serum and/or plasma separation tube devices on the market. That material is taught and claimed in U.S. Pat. No. 4,101,422 issued July 18, 1978.
However, the present polyester gel serum separation tube requires, for example, special manufacturing equipment to prepare the gel and to fill the tubes. Both processes require rigid controls. Moreover, the shelf-life of the product is limited in that globules are sometimes released from the gel mass or network. These globules have a specific gravity that is less than the separated serum and will float in the serum and can clog the measuring instruments, subsequently, during the clinical examination of the sample collected in the tube.
Moreover, while the gel is chemically inert to blood samples, if certain drugs are present in the blood sample when it is taken, there can be an adverse chemical reaction with the gel interface.
With this invention, by contrast, a mechanical separator is utilized which is non-temperature dependent during storage and shipping, is more stable to radiation sterilization, and eliminates the need for a special transport tube which is required for gel separation devices as discussed above for improved barrier integrity during transportation. The arrangement herein utilizes a dual component mechanical assembly arranged to move in an evacuated tube under the action of centrifugal force in order to separate the two portions of the sample.
The assembly includes a substantially rigid core component which nests within a cup-shaped elastomer component. The solid component, under certain operating conditions, is movable within the cup-shaped component. The two components operate together, and complement each other under the differing pressure differentials which are inherent in serum separation tubes, to provide alternating dual seals and open flow paths in response to those pressure differentials. As such, the arrangement herein provides a much more precise division between the two portions being separated from the original sample introduced into the tube.
Before describing this invention in more detail, it should be well to note that the dual component device of the invention herein has a conventional specific gravity range within between about 1.03 and 1.09, and more specifically within the range of between about 1.05 and 1.06 so that the device will come to rest under centrifugal force substantially at the border between the heavier and lighter phases of the sample under consideration.
In addition, the central core portion of the dual component device may be comprised of a substantially rigid moldable thermoplastic material such as polyvinyl chloride, polystyrene, polyethylene, polypropylene, polyesters, and mixtures thereof, with a limitation being that the material is inert to the sample introduced in the assembly of the invention so as not to interfere with any desired subsequent testing. The cup-shaped portion, in turn, may be comprised of any natural or synthetic elastomer or mixtures thereof, with, again, the limitation concerning being inert to the sample of interest. The stopper may be comprised of similar elastomer combinations.
While the invention is directed to evacuated tubes in order to facilitate introduction of blood samples from the vein of a patient, it will be understood that the container in accordance with this invention does not necessarily need to be evacuated.
Other objects and advantages of this invention will be apparent from the following description, the accompanying drawings, and the appended claims.